how to snap 2 specific points
Basically you want to use the 'Snap with Active' part of the snap feature. The active element is highlighted white by default instead of orange, and it is the individual vertex/edge/face you most recently interacted with. If you need to set your active vertex to something new, deselect and reselect that vertex.



Then it's just a simple matter of selecting the correct active vertex and snapping your mesh into place.